Support OS X 10.10.

I think we can get around this by explicitly setting the homebrew user to the build user before we include_recipe in [omnibus::_compile](https://github.com/opscode-cookbooks/omnibus/blob/72e9ab5bd9cc4e06782328e0de436e7eed703d46/recipes/_compile.rb#L36):

```ruby
node.default['homebrew']['owner'] = node['omnibus']['build_user']
include_recipe 'homebrew::default' if mac_os_x?
```

If we still need this directory resource we should not hardcode the owner to `vagrant` but use the value from `node['homebrew']['owner']`:

```ruby
directory '/usr/local/lib' do
  owner node['homebrew']['owner']
end
```